Impulse direction-finding receiver



Aprii 8, 1941. e. ULBRICHT IMPULSE DIRECTION-FINDING RECEIVER Filed May28, 1958 lnnentor Gunther ULbricht (Zttorneg Patented Apr. 8, 1941 resUNITED IMPULSE DIRECTION-FINDING RECEIVER Application May 28,1938,-Serial No. 210,596 In Germany May 31, 1937 2 Claims.

In order to practice direction-finding with the use of waves, no matterhow polarized, recourse is had quite often to impulse direction-finding.This'method is predicated upon the use of transmitter impulses which, inthe direction finding receiver, after having been amplified areoscillographed, in most cases so that first an upright pattern results.But if, then, in addition to the sending impulses of the direct orground wave, reflected impulses due to the space or sky wave (echoes)put in an appearance, the main impulses and the echoes may bedistinguished from one another in that, owing to the dilference in thelength of path of the direct and the reflected rays, the impulsepatterns of the chief impulse and of the echoes are separately visible.If the indicator device consists, for instance, of a Braun tube, thenthe two impulses, that is, the groundwave impulse and the space-waveimpulse, will be observed adjacent each other. In the methods known inthe art the direction-finding loop is turned until the pattern set up byground-wave impulses disappears.

Now, suggestions have been made in the prior art adapted to takebearings by ear rather than by eye by the use of opticaldirection-finding means as here mentioned. With this end in view,automatic volume control has been suggested which, upon the arrival ofthe main impulse causes the direction-finding receiver to be blocked fora short instant so that the impulse echoes are rendered ineffective.Hence, the time constant of the automatic volume control or gainregulation must be so brief for the blocking action that the gain willbe decreased to a sufficient degree during the time intervening betweenthe main impulse and the first impulse echo. 0n the other hand, thetime-constant of the unblocking action must be so chosen that, onarrival of the main impulse full sensitiveness has been restored.

In such an automatically regulated impulse direction-finder, however, itis not yet possible to eifect minimum signal strength direction-findingby acoustic means; on the contrary, it is still imperative to use aBraun tube screen for the recording or reading of the signal. Theunderlying reason is that the impulse frequency is too low (say, around50 cycles per second) so that there results no readily audible note.other hand, however, it is not feasible to shift the impulse frequencyupward inside the tonefrequencyv range for this would result indisturbances in all receiver sets in the neighborhood as a result of theoperation of these impulse On the transmitters. Practical experimentshave demonstrated that it is entirely impossible to choose the impulsefrequency, say, at 300 cycles per second, since the broad frequency bandof these impulses would fall directly into the audible.

suppress pensated by incoming ground-wave impulses.

The basic idea of the invention shall be explained by reference to theappended drawing in more detail. Fig. 1 is a. schematic diagram used indescribing the invention; Fig. 2 is a schematic circuit diagram of theinvention; and Figs. 3 and 4 are graphs descriptive of the operation ofthe device.

In Fig. 1 is shown an amplifier tube R the grid of which is fed with thetone-frequency voltage U0 which, for instance, may be of 1000 cycles persecond. Normally, the grid is subject to a marked constant negativebiasing potential Eg so that in the plate circuit of the tube upon whichthe positive potential Ea is impressed, no sound will be audible in thetelephone T connected to the output transformer U. Indeed, it is onlywhen the biasing voltage Eg is cut down to zero, say, by beingneutralized by a potential of opposite polarity, that thesound-frequency alternating potential will be amplified and renderedaudible in the telephone.

Now, according to the present invention, compensation or neutralizationof the biasing voltage Eg is to be eifected by causing the opening ofthe blocked tube by the incoming impulse signals (or signal impulses).An arrangement of this kind is illustrated in Fig. 2, where R1 the radiofrequency rectifier tube is connected to act as a plate detector. If,then, radio frequency impulses reach the grid of this tube R1, audiofrequency impulse signals will-be caused to arise across the outerresistance Ra which is shunted and bridged for radio frequency by thecondenser C1, the said audio frequency impulses having a polarity asindicated in Fig. 2. These signals cause the unblocking of the audiofrequency tube the impulse frequency of, say, 50 cycles per sec ond. Thenote of 1000 cycles per second sounds somewhat raucous, but it isaudible, so that by turning the direction-finder frame the point ofminimum signal strength is readily determinable.

It will be found convenient to reduce the coarseness of the note bytuning the output transformer U2 to the auxiliary frequency of 1000cycles per second.

If by the aid of a rectifier G which in series with condenser C1 isparalleled to the outer resistance Ra, provision is'rnade that thecondenser CI is rapidly charged, but discharged only at a slow rate ofspeed, still further improvement of the note is possible. The chargetime by suitable choice of the value of the resistance r may be made sothat CI, in the interval between two impulses, will just be discharged.Where conditions are as stated, the audio frequency which arises at theheadset T2 has a form as plotted in Fig. 4. If the duration of an'impuls'e'signal is less than a period of the auxiliary voltage U0, theincrease of the charge time of C1 must be adopted as shown in Fig. 4.

I claim as my invention:

1. A detector for impulse waves including a source of audio frequencycurrent, a thermionic tube including a cathode, a cathode lead includinga resistor and a connection to said source of audio frequency current, arectifier shunted by a second resistor connected in series with acondenser, said rectifier and series condenser being connected acrosssaid first mentioned resistor, and an audio amplifier effectivelyconnected across said first mentioned resistor and said audio frequencyconnection.

2. In a detector of the character of claim 1, means for biasing saidaudio amplifier to cut off.

' Gt'iNTHER ULBRICHT.

